Simplest Way To Do Dynamic View Models in ASP.NET MVC 3

Question

Caveat: This might be an inappropriate use of C#'s dynamic keyword and I probably should be using a strongly-typed view model, but...

I'm trying to avoid creating a strongly-typed view model by passing a C# 4 dynamic type to my view. I have this in my controller:

    public ActionResult Index()
    {
        var query =
            from fr in db.ForecastRates
            join c in db.Codes
            on 
                new { Code = fr.RateCode, CodeType = "ForecastRate" }
            equals 
                new { Code = c.CodeValue, CodeType = c.CodeType }
            select new
            {
                RateCode = fr.RateCode,
                RateCodeName = c.CodeName,
                Year = fr.Year,
                Rate = fr.Rate,
                Comment = fr.Comment
            };

        // Create a list of dynamic objects to form the view model
        // that has prettified rate code
        var forecastRates = new List<dynamic>();

        foreach (var fr in query)
        {
            dynamic f = new ExpandoObject();

            f.RateCode = fr.RateCode;
            f.RateCodeName = fr.RateCodeName;
            f.Year = fr.Year;
            f.Rate = fr.Rate;
            f.Comment = fr.Comment;

            forecastRates.Add(f);
        }

        return View(forecastRates);
    }

...and this in my view (I'm using MVC 3's Razor view engine):

        @inherits System.Web.Mvc.WebViewPage<IEnumerable<dynamic>>

        ...

        <tbody>
            @foreach (var item in Model) {
            <tr>
                <td>@item.RateCodeName</td>
                <td>@item.Year</td>                            
                <td>@item.Rate</td>
                <td>@item.Comment</td>
            </tr>
            }
        </tbody>

I don't like how I iterate through the LINQ result to form the List of dynamic objects.

I'd like to initialize each ExpandoObject inside the LINQ query, but that doesn't seem to be supported.

I tried casting the the query result as List, but that didn't work because you can't convert anonymous type to dynamic.

What don't you like about the way you're iterating? And why are you trying to avoid using a strongly-typed view model? Oh, and you definitely *can* convert from an anonymous type to dynamic, so I'm not sure what your last point is trying to say... Are you talking about the lack of variance in `List`? — Jon Skeet, Sep 21 '10 at 08:47
I just don't want to iterate to keep it a little DRYer (want to do it all in the LINQ query). I want to avoid using a strongly-typed view model and use dynamic instead because I don't want to repeat stuff that's in the model (and because I'm a wannabe Ruby developer doing C# at my job :). Though, maybe I could subclass the model to form the view model? Yes, I want to convert the result of the query to List (is this possible?). Thanks! — Derek Morrison, Sep 21 '10 at 10:02
Have a look at 'Clay'. See my answer to previous question: http://stackoverflow.com/questions/3758157/asp-net-mvc-having-one-model-for-all-views/3758368#3758368 — Clicktricity, Sep 22 '10 at 11:50

score 4 · Answer 1 · answered Sep 22 '10 at 06:53

Like you said, it's not supported. (I'm not saying dynamic View Models aren't supported - I'm saying what you're trying to do is not)

You could probably neaten up the LINQ query, but in the end your best bet would be to simply create a custom View Model. Seriously, it will take you about 30 seconds to do that.

I know dynamic is new and cool and everything, but your code will be a lot neater and easier to maintain if you just stick with a custom View Model in this case.

I would only go with a dynamic View Model in the very simple scenarios - most of the time you probably want to stick with what we've been doing all along - custom View Models.

Buildstarted · Answer 2 · 2010-09-22T14:20:21.233

Ok, you could do the following, but I wouldn't recommend it. Create a static method similar to the following

public static IHtmlString DisplayProperty(object obj, string property) {
    return new HtmlString(TypeDescriptor.GetProperties(obj)[property].GetValue(obj).ToString());
}

Then in your cshtml file make the following call (make sure to using your proper namespace)

<tbody>
    @foreach (var item in Model) {
    <tr>
        <td>@DisplayProperty(x, "RateCodeName")</td>
        <td>@DisplayProperty(x, "Year")</td>                            
        <td>@DisplayProperty(x, "Rate")</td>
        <td>>@DisplayProperty(x, "Comment")</td>
    </tr>
    }
</tbody>

I wouldn't recommend this though but it is a solution to your problem that doesn't require a model.

Simplest Way To Do Dynamic View Models in ASP.NET MVC 3

2 Answers2

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